Bioaerosols have a crucial role in healthcare-associated infections, especially in the intensive care unit (ICU). Previous knowledge regarding their role was usually derived from investigations with a limited sampling size in ICU. To explore the influencing factors of bioaerosol concentration in the ICU under various conditions, a field study was carried out in an ICU of a hospital, including a one-week measurement and a 24-h continuous measurement that was conducted in winter and summer, respectively. Effects of outdoor particulate matter (PM) concentration and the indoor occupant number on bioaerosol concentrations in the ICU were evaluated during these two seasons. Results revealed a positive correlation between bacterial and indoor PM concentrations, as well as the trend that indoor PM concentration varied with changes in outdoor PM concentration and the indoor occupant number. In conclusion, outdoor PM concentrations and the indoor occupant number, as well as particle sizes, were critical factors that affected PM concentrations in the ICU; the dominant role was determined by the outdoor PM concentration. This study contributes to a better understanding of the effects of environmental and human-related factors on air hygiene in ICUs, providing a guide for environmental control to minimize nosocomial infections in hospitals.
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